A 175 m. long train is travelling along a straight track what a velocity `72 km^(-1) h`. A bird is flying parallel to the train in the opposite direction with a velocity `18 km^(-1) h`. The time taken by the bird to cross the train is

Options

A. 35 s
B. 27 s
C. 11.6 s
D. 7 s

Answer

D

Explanation

Velocity of train,
`v_T` = 72 km/h = `72 xx 5/18 m/s` = 20 m/s
Velocity of bird, `v_b = 18 (km)//h = 18 xx 5/18 m//s = 5 m//s`
Since bird is flying parallel to train in opposite direction.
`therefore`Relative velocity of bird w.r.t train = `v_B + v_T` = 25 m/s
Train's length = 175 m
Time taken by the bird to cross the train is `= 175/25 = 7 s `